Briefly, a fluidized bed consists of a mass of finely divided particles contained in a chamber through which a gas is passed. Usually the particles are heated. If the velocity of the gas entering the bed is properly adjusted, the particles separate and move about in a random manner such that the entire bed behaves like a liquid. Such apparatus is well known and its fundamental behaviour has numerous applications. A typical such bed is disclosed in U.S. Pat. No. 3,677,404 owned by the assignee of the present application. For optimum performance it is important that the gas be dispersed uniformly across the mass of particles contained in the chamber. In general this is accomplished by means of a plate having ports therethrough located at the bottom of the chamber and so constructed and arranged as to diffuse the gas flowing through the plate and into the bed. Uniformity is attained by having sufficient and approximately equal pressure drop resistance through each opening in the plate and by having the openings uniformly arranged in the plate to require approximately equal flow rates across the entire plate area. In addition to the requirement of uniformity, a suitable distributor plate must have the property of permitting little or no passage of particulate matter from above the distributor plate, against the flow of gas phase, to the plenum chamber volume below the distributor plate.
In a typical configuration, the fluidizing gas enters a plenum chamber generally co-extensive with the horizontal extent of the bed and for distribution over the area of the bed by means of a diffusion plate. The gas rises through the bed during which liquid-like behavior is imparted to the particulate medium. The spent gas exits through a flue at the top of the chamber.
A variety of diffusion plate configurations are in use, varying from a simple metallic plate with small holes drilled therethrough to more involved structures including bubble caps and perforate baffles, various pipe and capillary tube configurations, as well as such specialized material as porous metal plates and porous ceramics.